It's a bad idea to bring Vieira back. It would degrade his transfer value whenever on the bench, and when not on the bench, we'd wish he were. We'd frankly be desperate for him not to play in any significant contest.
Ethan Nwaneri is better than him at every aspect of the sport for one thing.
We need to stop this practice of pretending Vieiras can be Trossards. The latter's a "difference maker", Vieira is not.
Only time he might be for us is when he's passing his prime and has grown a yard in grit and wisdom while being a load-bearing player for a lesser club—at that stage, if his record fits the need, you bring him in at a cut price and have him fill out the numbers.
Thing is, I can't ever see that happening with him.